Method of treating metals



June 8, 1937.

G. M. CROFT ET AL METHOD OF TREATING METALS Filed Oct. 11, 1934 4 Sheets-Sheet 1 hweizfarsz- GEO/Q65 M. CROFT and JoH/v ,4. HUN TEE.

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METHOD OF TREATING METALS Filed Oct. 11, 1954 4 Sheets-Sheet 3 /m/ 5 m v \D 4 H E 7 I v uw i F Q,

June 8, 1937.

G. M. CROFT ET AL METHOD OF TREATING METALS June 8, 1937.

Filed Oct. 11, 1934 4 SheetsSheet 4 lll' ll il-i lyweiziarss (350/965 M. Geo/ T and Z .JoH/v #7. HUNTER.

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Patented June 8, 1937 UNETED STATES 2.083.482 V METHOD or TREATING METALS George M. Croft, Dormont, and John A. Hunter, Ben Avon, Pa, assignors to American Sheet and Tln'llate Company, a corporation of New Jersey Application October 11, 1934, Serial No. 747,946

' 1 Claim. (01. 148-18) 6 This invention relates to a novel method of treating metals, and more particularly to the deoxidizing and bright annealing thereof.

In the manufacture of metals, and particular- 1y highly finished sheet'metals such as are intended for subsequent use as automobile bodies,

commercial tin plate and the like, it is highly desirable to bright anneal or deoxidize the same.

It'has been the practice in the past to deoxidize or reduce hot mill scale and other superficial surface oxides and bright anneal (to prevent reoccurrence on the surface of the highly finished sheet metal of oxides) by introducing hydrocarbon-bearing gases into a container in which the metal is disposed. The gas is usually 7 either natural, coke-oven, coal or producer gas,

. and even the heavier hydrocarbons (such as propane and butane) in either a gaseous-or liquid state.

These gases contain free oxygen and moisture and vary widely in composition. Due to this, they are readily broken down and invariably result in carbon or soot being deposited, in addition to whichthe oxygen and water causes blued,

. 2 or otherwise discolored, metal. These conditions are, of course, highly objectionable but had to be contended with as the annealing, or softening, of the metal is necessary. The complete deoxidation (reduction of oxides etc.) and bright an- 30 nealing of metals (prevention of reoccurrence of oxides, etc.) has heretofore been impossible if raw hydrocarbon gases are used.

It is one of the objects of theinvention to provide a novel method of treating metals .which 35 will effect the complete elimination of surface defects heretofore encountered in annealing operations.

Other objects will be apparent after referring to the drawings, in which:

Figure 1 is a schematic layout.

Figure 2 is a plan of a part of the apparatus. Figure 8 is a view on the line III-III of Fig? ure 2. Figure 4 is a view on the line IV- -IV of Figure 2.

Figure 5 is an end elevation of the part of the I apparatus shown in Figures 2, 3, and 4. I v Figures 6 and 7 are enlarged fragmentary details. 9 The gas reforming apparatus preferably used in carrying out the method of the invention comprises, in part a box or furnace A which is rectangular in shape, having ends I, sides 2,

bottom Iyand top 4, all of suitable steel welded or bolted together. The box or furnace A is lined with a suitable insulator brick 5 and mounted on supporting legs 6. A lifting lug 8 is attached to each corner of the box 4 to permit its easy transportation as a unit by means of 5 a crane (not shown).

Within the insulated box A are vertical tubes 9 connected in series by tubes Ill. b These tubes 9, and connecting tubes l0, are-of a heat resisting alloy such as chromium or chromium-nickel 10 hearing steel which is capable of withstanding the high temperatures to which they are subjected. The number of vertical and connecting tubes may vary, depending on the amount of hydrocarbon gas that is to be forced therethrough, 15 as well as the temperatures to which the gas is exposed. The ends of the tubes 9 extend through the top 4 and bottom 3 of the box A and are normally closed, as by caps I I. These tubes 9 are vertically suspended by means of bolted support- 20 ing clamps l2, which encircle them at the top 4 of the box-A. The entire length of the tubes 9 and III, with the exception of the first tube, which is indicated at 9', may be filled with any substance 13 such as crushed brick, refractory, or any such medium whose bond will not deterlorate and which will -be capable of withstanding high temperatures and yet offer a maximum contact surface for the gases. It has been found from experiment that any first quality fire brick that will pass through a 1%" screen is the most suitable medium due to the fact that it efiiciently permits the transmittal of heat to the gas to be reformed, and at the same time is neutral with respect to any reaction with steam which is admitted in the process.

The 'inactiveness of the refractory is also desirable in that it will allow the introduction of an excess amount of steam which is good insurance against plugging up of the box A by carbon that 40 might precipitate from the gas during the reforming process. However, any heat resisting metal which will give maximum heating area and stand up as long as refractory material will give equal results. If the volume of gusto be treated is exceedingly great this refractory may be dispense'd with and the tubes used inv an empty condition. a

The tubes 9 and It are heated by gas burners l4disposedassh0wn (Figures3and4) through 9 the ends I of the box A. The heat input of the burners I4 is automatically, oimanually, controlled by a pyrometer II which is disposed in'the exit tube which is indicated at l". The waste gas,

or products of combustion, escape from the box A through vents l6 disposed on the ends and sides I and 2 adjacent the roof of the furnace.

The raw hydrocarbon bearing gas is introduced into the box A through an inlet pipe l1. However,

before it reaches the first tube 9 within the box it is caused to mix with an excess of steam which is injected through a pipe Ill. The position of this steam inlet with relation to the gas burners I4 is best shown in Figures 5 and 6, and is slotted as at I8 to insure a homogeneous mixture of gas and steam. I

The mixture of raw hydrocarbon bearing gas and excess steam is thusexposed to high heat (about 1800 degrees-1900 degrees F.) as-it travels through the tubes 9 and III. This causes the reformation orbreaking down of the basic constituents of the gas and producing principally hydrogen (H2) and carbon monoxide (CO) in varying but controllable amounts.

The amounts of these reformed gases and the minute presence or total absence of oxidizing mediums depend on the temperature to which the hydrocarbon gases are subjected and the ultimate use of the gas as hereinafter described in detail.

At this stage of the process carbonin the form of soot may be precipitated out of the gas, but the carbon in the gas reacts with the excess steam. Any free oxygen is taken up by the new gaseous mixture and excess steam plus water vapor in the raw gas may precipitate in the last or exit tube 9'' to be suitably and periodically drawn off by a collecting bulb and shut-oi! valve ll. While such a condition is exceptional it is, however, possible and therefore is anticipated.

Following the heating and breaking down of the hydrocarbon gas mixture within the box A or reforming furnace the reformed gas is conducted through an exit pipe 20 to a cooler B. This cooler B is for the purpose of condensing and removing any water vapor and excess steam that may still be retained by the gas, and is standard equipment such as is ordinarily used with air compressors; utilizing ordinary mill water as a cooling medium. In the event that the mill water temperature runs between '70 degrees-100 degrees 1''., especially during the summer season, it has been found desirable to pass the gas coming from this cooler through any standard refrigerating machine which is adjusted to chill the gas preferably to 35 degrees-40 degrees F. Suitable drains are provided on both types of coolers for draining oi! the condensed water vapor thus extracted from the gases as chilled.

At this point it has been found that the chilled reformed gasescontain principally hydrogen, carbon monoxide and some methane together with small amounts of water and carbon dioxide. A typical analysis might for example indicate: 50-60 per cent hydrogen (Ha) 35-40 per cent carbon monoxide (CO) and remainder being methme (CH4) water vapor and steam (H20) and carbon dioxide (CO2).

If this gas is to-be used in the deoxidizing or reducing of oxides on sheet metal (such as hotmill scale and the like) the presence of these small amounts of water vapor and carbon dioxide have not been found to work a hardship at the relatively high temperatures (1200 degrees F.1500 de-.

grees F.) which may be used in the deoxidizing treatment. However, if the gas is to be used in the presence of highly finished sheet, or strip (such as metals cold reduced on four-high cold reductionmills orthelike),it must be further treated so as to remove all gases except hydrogen, carbon monoxide and methane. To cause the removal of any water vapor, carbon dioxide, or any oxidizing media, the cooled reformed gases are again passedthrough the box or furnace A previously described. For this purpose a plurality of vertical tubes 2| and connecting pipes 22 are provided and connected in series in the same manner as tubes 9 and pipes l0.

These reheating tubes 2| are made of a suitable alloy andcontain charcoal 23 or a like substance capable of extracting from the reformed gases practically all of the water vapor and reducing carbon dioxide to carbon monoxide which may still exist. This gas which is further purified" by its passage through the charcoal-containing tubes may well be used not only for the bright annealing of highly finished or surfaced sheet metal but also for deoxidizing, in which event a substantial improvement of product is obtained over the otherwise unpurifled gas. The gas is passed through these'reheating tubes 2| and connecting tubes 22 from the cooler B by means of feed-pipes 24.

Following the exit of the reformed and purified gas from the cooler B and the tubes 2|, it is led through pipes 25 to a manifold 26, from where it is distributed to a plurality of annealing boxes 21 which are schematically shown in Figure 1. These.

annealing boxes 21 are of the conventional type comprising a base 28 and cover 29 of cast steel, or iron. The'pile of metal, such as sheets Ill-or coils 3|, are placed on the base 28,:the cover 29 placed thereover and a sand seal. 32 maintained therebetween to prevent the entrance of air. A plurality of tubes 33 lead from the manifold 20, under the covers 29 and through the sand seals 32; thus introducing the reformed gas into the presence of the'metal-to be heated. The use of the reformed and purified gas is favored as it bears not only further purification but is in a preheated condition which shortens the desired heat cycle of the annealing boxes 21. The tubes 33, which lead from the manifold 26 under the covers 2s and through the sand seals 22, are provided with suitable quick-detachable connections, as at ll.

If the metal is free from any metallic surface defects such as scale, pickle stains, or any degree of oxidation, the treatment confines itself to bright annealing. Bright annealing as accomplished by the use of the improved gas mixture is carried out at a relatively low temperature (950 to 1200 F.), the presence of the gas being only for the purpose of maintaining the bright, unoxidized surface and preventing the reoccurrence of oxides. The heat to which the sheets are subjecttd is, of course, for the purpose of annealing. The reformed gas should containlittle or no carbon dioxide, oxygen or water vapor, and if such oxidizing media are present in very small amounts they will be ineffectual due to the preponderant presence of hydrogen.

The purified and reformed gas, as it comes from the purifying and charcoal-containing tubes 2| contains approximateLv 61 per cent hydrogen (H approximately 35 per cent carbon monoxide (CO), the remainder of the gas containing principally methane (CH4) It is to be understood bythose skilled in the art that these percentages of hydrogen, carbon monoxide and methane will vary somewhat, depending on the type of raw gas or liquid hydrocarbons to be reformed and the time and temperatures to which they are subjected. Thus, for

:1820 F. in the presence of excess steam in the box or furnace A, as previously described.

The same percentages of hydrogen and carbon monoxide as utilized in the bright anneal of metals just described can be applied equally well in the deoxidizing treatment. This deoxidizing treatment is limited in this specific example to boxes or closed containers and involves relatively high heat treatments, such as, for example, 1200-1500 F.

The entire gas reforming equipment may. be automatically controlled or operated by inserting specified size'orifices (not shown) in the individual lines to each annealing box 21 and maintaining a constant pressure in the manifold 26 by means of a suitable gas pressure regulator. The flow to the boxes 21 will vary in accordance with the porosity of the sand seal 32 and the automatic temperature control will maintain a constant temperature in the furnace or box A. The

steam regulator may be set to deliver a constant pressure.

The deposits of carbon or soot on the metal are thereby eliminated, the objectionable oxides on such metal are completely reduced and no fur ther discoloration or reoccurrence of oxides on the metals is possible through the more or less complete absence of oxygen and/or water vapor in our hydrogen-carbon monoxide mixture.

We find that, by the use of this high hydrogen and high carbon monoxide gas mixture produced from reformed hydrocarbons, the ultimate surface of the sheet metal heated in the presence thereof is extremely well adapted to receive protective and decorative coatings such as lacquers, paints and lithographic mediums. This metal surface having been exposed to gas under heat apparently takes a thinnenand more uniform coating of various paints for protective or decorative purposes than metals whose surfaces have been cleaned by raw gases or acids.

We further find that such reformed gases react on and remove oil from the surface of metals, such as sheet or strip metal, piled flat, or in coils, which have been previously subjected to a processing step which left a film of oil (lubricating or preservative) upon their surfaces. It has heretofore been practically impossible to remove this oil film without causing discoloration, especially of sheet or strip metals as bright annealed. I

While we have shown and described one specific embodiment of our invention, it will be understood that we do not wish to be limited exactly thereto, since various modifications may be made without departing from the scope of our invention, as defined in the following claim.

We claim:

A method of treating metals which includes heating the same and subjecting the heating metal to a broken down and reformed gas consisting of approximately 61 per cent of hydrogen, 35 per cent of carbon monoxide and the remainder methane, said gas being devoid of any infiuential oxidizing medium.

GEORGE M. CROFT. JOHN A. HUNTER. 

